Acanthamoeba pathogenicity for corneal cells

Comparison of the relative susceptibility of human keratocyte and corneal epithelial cells to Acanthamoeba castellanii.

Primary cultures of the mammalian cells were utilised at equivalent concentrations throughout the co-incubations. Preliminary experiments involved visual estimation of the effects of 10-fold dilutions of Acanthamoeba trophozoites after various time intervals. Formal quantative assessment was performed by image analysis of the respective effects of the Acanthamoeba at a concentration of 10(6)/ml/well following 3, 6, 9 and 24 h of co-incubation.

Epithelial cells were relatively resistant to the cytopathic effects of Acanthamoeba throughout the experiments course at all concentrations tested: the cut-off point, below which no effect was observed, was also greater. Formal assessment by image analysis confirmed these impressions while revealing that the relative resistance of epithelial cells was confined to the initial phases of co-incubation. For both mammalian cell types the first observable sign of cell damage was cell shrinkage with the formation of retraction fibres and gaps.

The relative resistance of epithelial cells to Acanthamoeba may be due to difficulty in initiating attack of a monolayer with tight junctions between cells. These results provide circumstantial evidence of the importance of the corneal epithelium in the prevention of amoebic invasion.

The relative susceptibility of cultured corneal epithelial cells and keratocytes were compared as regards both the concentration of amoebae required to produce obvious cell damage and the area of cells destroyed for a given concentration at various time intervals. The epithelial cells were more resistant than keratocytes with respect to both factors, at least early in the co-incubation period. This may be related to the different growth patterns of the cell types as epithelial cells form a monolayer connected by tight junctions and indirectly supports the idea that the epithelium forms an important barrier function against invasion in vivo.